2 



Prof. W. N. Hartley and A. K. Huntington. 



stone, from whom we obtained many oils which he had previously 

 examined, Mr. Farries, of the firm of Burgoyne, Burbidges, Cyriax, 

 and Farries, Dr. Septimus Piesse, and Dr. W. A. Tilden, who has- 

 given us some remarkably pure preparations derived from turpentine 

 and from Portugal essence. The diagrams which explain the optical 

 characters of the various substances examined, and particulars concern- 

 ing which here follow, were made in the same way as those appertaining- 

 to the Parts I and II of this research. The wood cuts made from our 

 diagrams have had the light and dark parts reversed, so that they 

 differ from the lithographs of the same character published in the- 

 Phil. Trans., Part I, 1879: they have of course been greatly reduced 

 in dimensions, but not all to the same scale. The layer of liquid 

 examined was 15 millims. instead of 19 millims. thick. 



We have found that the following essential oils and hydrocarbons 

 transmit continuous spectra : — 



The four isomeric terpenes (Diagrams 1, 2, 3, and 4) prepared by 

 Dr. Tilden— 



Australene, from common turpentine obtained from the Finns 

 Australis. Boiling-point 156-157°, specific gravity at 0° C. =0-876, 100 

 millims. rotate the polarised ray of light 22° to the right. — Undiluted, 

 this hydrocarbon transmits rays lying between the 12 and 17 Cd. lines.. 

 Solutions of the substance in alcohol were examined containing y^o* 

 -eitoi ToVo> ail d -5 oVo °f their volume of the terpene. No absorption 

 band was seen. 



Terebene* prepared from American turpentine by precipitating with 

 sulphuric acid. Boiling-point 156°, specific gravity not ascertained, 

 optically inactive. — The spectrum of the undiluted substance was much 

 the same as that of australene. Further examinations were made of 

 solutions containing Tt ^, T¥ Vo of the volume of the 



liquid. The spectrum was continuous. 



Terebenthene, from French turpentine. Boiling-point 156-157°, 

 specific gravity at 0° C. = 0'876, 100 millims. rotate the polarised ray 

 27-^° to the left. — The transmitted rays were much the same as before. 

 Solutions containing T \, y^, T ± ru , ^Vo, and -^Vo of their volume of 

 the substance were examined. 



Hesperidene, from Portugal essence. Boiling-point 176-177°, specific 

 gravity at 0° C. = 0*859, 100 millims. rotate the polarised ray 96° to the 

 right. — Dilute solutions containing -^q, and -5 oV o °^ their volume 

 of the liquid were photographed. 



The four diagrams drawn from the photographs obtained from these 

 substances show the rays transmitted by 15 millims. of the liquid alone 

 and when diluted; all rays to the right of the curves are those 

 absorbed by the liquid, while those to the left are transmitted. 



* This substance has been shown to be chiefly camphene. See " J. Chem. Soc," 

 Trans., Vol.35, p. 758, 1879.— W. N. H., June,'l880. 



